Over the years, a considerable amount of effort has been directed to developing laser resonator assemblies. For commercial applications, resonator assemblies should be stable, sturdy, easy to build and relatively low in cost.
In the field of diode pumped solid state lasers, the resonator elements are often supported in a machined or cast fixture. More specifically, metal fixtures have been designed for receiving and supporting the laser gain medium and resonator mirrors. Examples of such resonator assemblies can be found in the following U.S. Pat. Nos. 4,730,335; 4,731,795; 4,890,296; 4,653,056; 4,656,635; and 4,665,529.
All of the latter designs have a number of drawbacks. For example, the machined or cast parts require relatively complex fabrication steps with close mechanical tolerancing. In addition, common metals which are used to form the assemblies have relatively high coefficients of thermal expansion. For example, the coefficient for aluminum is 24.times.10.sup.-6 /C.degree. while brass is 19.times.10.sup.-6 /C.degree.. While some metal compounds, such as Invar, have much lower coefficients of thermal expansion, they are difficult to machine and are not generally used for these applications.
When the more common metals such as brass or aluminum are used to house the laser elements, the resonator dimensions will vary significantly with temperature changes. As the resonator dimensions change, the laser is subject to mode hops. These mode hops can result in amplitude instabilities in intracavity frequency doubled lasers and discontinuities in the frequency tuning for tunable single frequency lasers.
Accordingly, it is an object of the subject invention to provide a new optical assembly which is mechanically rigid.
It is another object of the subject invention to provide an optical assembly which has a low coefficient of thermal expansion and therefore is very stable with respect to temperature fluctuations.
It is a further object of the subject invention to provide a resonator assembly which has a coefficient of thermal expansion matched to the gain medium so that the change in mirror spacing causes a shift in the cavity axial mode frequency which tracks the frequency shift with temperature of the gain medium. This thermal matching allows continuous tuning of a single frequency laser by varying the temperature of the laser. The thermal matching also minimizes instabilities in a frequency doubled laser.
It is still another object of the subject invention to provide an optical design that is low in cost and easy to assemble.
It is still a further object of the subject invention to provide a mounting member for supporting an optical element wherein the mounting member is aligned with and transparent to laser radiation.